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Fig. 2. Speed and chemotaxis index during aggregation. (A) Wild-type AX3 and gc-null cells were allowed to aggregate on non-nutrient agar plates, and a movie of the aggregating cells was recorded (supplementary material Movies 1 and 2). The chemotaxis of the cells was analyzed from the time-point where cells first make a simultaneous movement surge in the direction of the aggregation centre (t=0 minutes) until the time-point where most cells are incorporated into streams (t=60 minutes). A representative cell in each frame is enlarged in the bottom frame. The arrow points in the direction of the aggregation centre, which is out of view. (B) The position of 25 cells was tracked throughout the duration of the movie. Cell tracks of three representative cells are shown. The tracks start at t=0 and are followed for at least 40 minutes. Unfilled dots were placed on the cell tracks representing the positions at intervals of 1 minute. Cells move in the direction of the aggregation centre, as indicated by the arrow. (C) The average chemotaxis index and speed of the cells was determined in each movie. The dotted lines indicate the progress of the minimum and maximum chemotaxis index, respectively, during the course of aggregation. The period where the minimum chemotaxis index increases with each subsequent wave is referred to as the `transition period'. (D) The waves of the chemotaxis index of aggregating cells during the transition period of two independent movies were averaged. Time on the horizontal scale is relative to the time-point of the peak of the wave. The 
CI that is indicated in the graph is the difference between the average of the lowest three points of the chemotaxis index both before and after the wave. (E) The number of protrusions in the front one-third and rear one-third of the cell was determined throughout aggregation. The graph shows the average number of pseudopodia during the first four waves and the last four waves of the movie. Error bars indicate the standard deviation.
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